17-year-old Rohan is expelled from the reputed Bishop Cotton School, Shimla boarding school along with three friends Vikram, Benoy and Maninder when they are caught by their warden watching an adult movie off campus.

Rohan returns home to Jamshedpur to a stern and abusive father and a 6-year-old half-brother, Arjun (whose existence Rohan hadn't known about), not knowing what's in store for him. His father forces him to jog every morning and race him at the last leg. Rohan then must work at his father's metal works factory and attend engineering classes at the local university immediately afterwards. His father's disappointment takes the form of verbal and physical abuse and constant humiliation. Rohan's kind uncle supports his ambitions of being a writer but his father will have none of it. One night he sneaks out of the house, takes his father's car and goes to a local bar. There he meets some seniors from his college who try to rag him but later become his friends. This - taking his father's car and drinking at the bar - becomes a regular habit.

An uninterested Rohan deliberately fails the exam so that his father will give up on him, leaving him free to pursue his dream of becoming a writer. At the same time, his father is summoned to school to take Arjun away because of something he has done. This causes his father to lose an important contract. Rohan comes home to a scene where Arjun is being rushed to the hospital for some unknown reason. His father says that Arjun fell down the stairs. Fearful of complicating matters, Rohan lies to his father and says that he passed his exams. His father then goes to Calcutta on an urgent business trip leaving Rohan to take care of Arjun in the hospital.

In the hospital, Rohan impresses a lot of people including doctors and nurses with his stories and poems. He befriends Arjun and discovers that he was beaten by their father after losing the contract. His father returns from Calcutta and finds that Rohan has failed the exams. Enraged, the father assaults Rohan in the night but apologizes the very next day. The next morning their father declares that he is going to marry again and decides to send Arjun to a boarding school while Rohan is supposed to quit college in order to work full-time at the factory. When Rohan's uncle offers to take Arjun in, he is belittled by Rohan's father for his impotency and thrown out of the house while Rohan pleads with his uncle to take him away. Furious about this, his father burns Rohan's diary where he has written all his poems. Some time later, Rohan's father introduces his new wife and step-daughter to Rohan. On his 18th birthday, his father gives him his watch, originally belonging to Rohan's great-grandfather and says that he should continue the tradition. Rohan calls his friend Maninder, who is living a successful and happy life with his friends in Mumbai and breaks down on the phone unable to say anything about his own life to his friends.

One day, Rohan takes all his frustration out on his father's car by a river but some policemen happen to see him in the act. He spends a night in prison after his father comes to know about the car and leaves him to his fate. He finds his to-be stepmother and her relatives in the house when he returns. Rohan learns from Arjun that he would be leaving for boarding school the next day. Rohan simply wishes him luck and prepares to leave home. On his way out, Rohan exchanges bitter words with his father in front of his guests and when confronted and aggravated by his father, punches him and runs away. His father chases Rohan through the streets on foot, but cannot catch up to him anymore. Rohan spends the night at his uncle's house. His uncle has a quiet word with Rohan in the night, it is implied that it is regarding Arjun's fate. The next morning Rohan returns to his father's house and finds Arjun waiting outside while his father has gone to get a taxi to take him to boarding school. Rohan convinces Arjun to go with him to Mumbai leaving the watch and note behind explaining his decision and warning his father not to look for them, with the threat of revealing his attacks on Arjun to the police. The movie ends with Rohan and Arjun walking away holding hands.

The film received positive reviews from critics on release. Bollywood Hungama gave the film 3.5 out of 5 stars, calling it "a simple, straight-forward film that doesn't need to be explained. It needs to be experienced."[5] Gaurav Malani of IndiaTimes rated it 4/5 "In an industry known to indulge in larger-than-life ‘flights of fantasy’, Udaan is one of those intermittent ‘coming of age’ films from Bollywood. Do not miss!".[6]Nikhat Kazmi of Times of India rated it 4/5 "Udaan is unconventional Bollywood at its biting best. The film is a moody, introspective and ekdum different look at teenage angst"[7] Pankaj Sabnani of Glamsham.com rated it 3.5/5 and stated that "The best part about Udaan is its simple yet heartrending & relatable story... Udaan surely passes with flying colours. It will linger on your mind for a long time to come."[8]Vinayak Chakravorty of Mail Today gave it four stars, saying: "The film documents subtly the great smalltown Indian dream that defines engineering as the only yardstick of success for boys." Mayank Shekhar of Hindustan Times rated Udaan 3.5/4 and of the view that "This is that rare, superior latter: a bleak beauty, a commendable debut."[9]Rajeev Masand of CNN-IBN gave it 4/5 and stated that it is"intuitively written and lovingly crafted, Udaan is packed with moments that will resonate with every viewer because they mirror real experiences."[10] Kaveere Bamzai of India Today rated it 4/5 and described it as "an extraordinary story told without veering into the maudlin. It's a tightly controlled drama without any melodrama."[11]Pratim D. Gupta of The Telegraph rated it 7.4/10 and calling it a "must watch".[12] Vivek Bhatia of Filmfare.com rated it as 3/5 and elaborated that "the strength of Udaan lies in its story telling, which is very real. As are the setting and the overall ambience."[13] According to film critic Subhash K. Jha, Udaan "gives us some great moments of cinema , done in shades that leave the camera lens far behind to romance the very core of middleclass life..."[14]

The music for Udaan is composed by Amit Trivedi and includes 7 tracks. The lyrics have been done by Amitabh Bhattacharya and Anurag Kashyap.[15] The film's music got overwhelming response from the critics. Amit Trivedi's rock & grunge style was highly appreciated whereas Anurag Kashyap's lyrical debut "Motumaster"'s lyrics had got good response. Amitabh Bhattacharya's lyrics in the other tracks were called "a classy act".

The film was officially selected to compete in the Un Certain Regard (A Certain Glance) category at the 2010 Cannes Film Festival.[2][3][4] Udaan was first Indian film to be part of Cannes' official section in seven years.[16]Udaan got screened in 40th Giffoni Film Festival for children's films in Italy[17] bagging Audience Choice Award along with the trophy for Best Music Score.[16] It has also been adjudicated as the Best Film and Motwane as the Best Director at the 17th Annual Star Screen Awards. Udaan won Best Narrative Feature at the Indian Film Festival in Los Angeles in April 2011.[18]